Field of the Invention
The invention relates to a transimpedance amplifier circuit having an inverting amplifier with an input that is supplied with an input current and an output that carries an output voltage, and a coupling member which is connected between the input and the output of the inverting amplifier.
In one such transimpedance amplifier circuit that is known, for instance, from the book entitled: Electronic Circuits--Design and Applications, by U. Tietze and C. Schenk, Berlin and Heidelberg 1991, page 97, an ohmic resistor is provided as the coupling member. Transimpedance amplifiers convert an input current into a proportional voltage and are therefore as a rule used for amplifying the currents produced by photodiodes. On one hand that current can be very low, such as 1 .mu.A, or very high by comparison, for instance 1 mA. That presents problems of dimensioning, which can be ascribed particularly to the ohmic resistor that is used in a feedback loop in the known construction.
The resistor must be small to prevent oversteering of the transimpedance amplifier at high currents. However, the input noise of the transimpedance amplifier then rises since smaller resistors generate higher thermal noise currents. Smaller resistors also cause a reduction in sensitivity, so that low input currents are lost in the noise. However, then the overall result is a severe limitation of the dynamic range of the transimpedance amplifier.
Transimpedance amplifiers with a wide dynamic range in any event have high basic amplification, so that they can generate a sufficiently high output signal even at very low input currents. The result, however, is an increased tendency toward oscillation when the input currents are high.